When making a magnetic tape recording in a recording studio, of a band or orchestra including many different instruments, it is usual to provide respective microphones for the instruments or for groups of the instruments, and to record the electrical signals from the microphones separately on respective tracks of a multi-track magnetic tape. The microphones may be of any of the conventional types, capacitor microphones for example, each mounted to produce electrical signals in response to air vibrations produced by playing of the instrument to which the microphone is directed. After recording, the recorded signals from the different tracks are mixed and re-recorded onto typically a twin track magnetic tape to produce a master tape from which a stereo gramophone record can be made. The mixing of the signals permits a desired balance between the relative amplitudes of the instruments to be achieved. For the mixing to be effective, it is desirable that the signals recorded on the different tracks of the multi-track tape are each representative substantially only of one of the instruments or a predetermined group of instruments, but in practice this is difficult to achieve for certain instruments, particularly drums and also stringed instruments such as pianos. In the usually cramped conditions of a recording studio, a conventional microphone positioned to detect sound produced by a piano usually also detects sound produced by adjacent instruments; this degrades the recording unless other measures are taken.
A similar difficulty arises when electrical amplifiers and loudspeakers are used to amplify a live performance of a band in a concert hall. Usually separate microphones are used for different instruments, and the signals therefrom are mixed selectively before being amplified and fed to loudspeakers in the hall. However, for certain instruments, the microphones tend to detect sound not only from the instrument to which they are directed, but also from adjacent instruments.
This problem is particularly serious for a piano, and a conventional microphone directed at a piano will respond not only to the sound from the piano but also to sound from adjacent instruments, with the result that it is often not possible to give the sound from the piano a desired prominence in the sound emanating from the loudspeakers.
In order to overcome these problems for a piano, a pick-up device has been devised which consists of a support member extending transversely of the strings of the piano, on which is mounted a series of magnetic pick-ups which produce electrical signals in response to oscillations of the strings when the piano keys are struck. The device is however relatively expensive due to the number of individual magnetic pick-ups required for the many strings of a piano. Also, the device requires a complicated adjustment prior to use because in order to obtain a uniform amplitude response for the different notes of the piano, the gains of the outputs from the numerous pick-ups need to be adjusted individually. Additionally, the pick-ups all need to be close to the strings in order to obtain a satisfactory response, which requires a delicate adjustment. Moreover, if the piano is moved, for example by being pushed on or off a stage, or by being transported in a truck between concert halls, the setting of the pick-up device becomes disturbed, and the time consuming and complicated adjustment often needs to be carried out after such moves of the instrument.